The present invention relates to a new and improved instrument which I have termed a "liquid consistency meter" designed for highly accurate measurement of the consistency of heavy liquids, semi-liquids, or semi-paste compositions. One practical and specific example of use of the improved instrument is for measuring high-consistency, water-based latex paints but is by no means limited to such an application. The instrument is capable of measuring extremely thick compositions with complete accuracy and all measurements are accurately reproducible. It can measure unthinned as well as thinned compositions. Heavy liquids, water or solvent based, even those with fibrous fillers added, or even those with small lumps can be accurately measured. Also asphalt or gilsonite heavy mixtures. The instrument is also useful for measuring ceramic frit mixtures, slurries, etc. Semi-liquid heavy oils and greases, or typical roof coatings, both water and solvent based, with or without fibrous additions can also be measured accurately. The instrument is also useful in the food industry in connection with processing of batters, sauces, ketchup, and the like. Other possible uses for the instrument are for measurement of the consistency of semi-liquid pigment pastes, resin solutions, semi-liquid printing ink pastes and other similar materials.
The instrument in accordance with the invention is not intended as a substitute for conventional flow viscosity measurements. Rather it is intended as a means for measuring compositions which have a high consistency beyond the normal scope of flow viscosity, e.g., in cases where flow viscosity measurements become ineffective due to the capillary and consistency differences between solvent-based and water-based mixtures.
To my knowledge, none of the 20 to 30 flow or eflux types of viscometers, including the well known "Zahn Cups" is capable of measuring the consistency of extremely heavy liquids, for example, unthinned latex paints, because a thixotropic condition, or false body, or both, exist in the latex paints as produced. Even though most of the latex paints now being marketed contain 50% of more of water, the consistency is so high that the material cannot flow through an orifice of normal size. Often, thickening agents are added to increase the thickness factor to a point where pigment settling cannot occur and this also prevents drips or runs when the material is applied to a substrate by conventional means.
Some rather elaborate and hence expensive viscosity measuring devices are known which can measure the liquid shear resistance of heavy liquids, e.g., U.S. Pat. No. 3,569,722 -- Denson -- granted Mar. 9, 1971, but such measurements have no relationship to my invention in the consistency meter to be described hereinafter in more detail. Shear-resistance of a heavy liquid, for the most part, is a direct result of the material's (non-volatile) content. A relatively thin material with a high pigment content can exhibit high shear resistance. In a certain sense, these instruments are affected by the element of viscosity, but by including the shear resistance as principal factor, they in no way indicate the actual viscosity of the material being measured.